The present invention relates to a device, which captures energy resident in the motion of ocean waves to rotate a generator and thereby generate electrical power.
A wave energy converter (WEC) captures energy from ocean surface waves, usually for electricity generation. Of the solar energy forms, the energy of the waves provides the highest energy density. However, prior attempts at wave power generation have not been widely accepted for various reasons.
Wave power is available in low-speed, high forces, and the motion of forces is not in a single direction. Most commercial electric generators operate at higher speeds, and require a steady flow of source energy. Furthermore any apparatus deployed on the ocean must be able to survive severe storms, raising the cost of manufacture and maintenance.
The key to commercial viability of wave technology is a competitive levelized cost of energy (LCOE). Wave power is competitive when the total cost of power generation is low. The total cost includes the capital costs, maintenance costs and electric power delivery costs, and this in relation to the electric power generated, determines the “life-cycle” cost of energy. It is therefore desirable to provide a method and apparatus of obtaining optimum energy extraction from ocean waves at the least cost for the generating system.
The system must have minimal impact on the marine environment, such as fishing grounds and beach shoreline and must not interfere with ocean navigation.
U.S. Pat. No. 4,851,704 to Rubi, titled “Wave action electricity generation system and method” discloses a wave action electricity generation system that includes a floating platform that supports the system components on the water. Wave motion energy is converted into mechanical energy and an electricity generator converts the mechanical power transfer strokes into electrical energy.
The converter includes a cylinder containing a lubricant, in opposed cylinder chamber portions, a first heavily weighted piston that is slidably and freely disposed within the body of the cylinder. The heavily weighted piston is slidably responsive to the wave motion energy of the body of water and is used to compress the fluid to produce respective compression power strokes in each of the cylinder chamber portions. The energy in the compression stroke is received by a second and third pistons located in the cylinder chamber portions that further produce power transfer strokes through the ends of the cylinder. The power transfer strokes associated with the first and second pistons are further converted by a geared transmission to rotary motion that turns a flywheel coupled to an electricity generator. The electrical energy produced is then distributed to a remote power station via a power transmission line.
U.S. Pat. No. 5,889,336 to Tateishi “Power generating installation” discloses a power generating installation located in a shallow water area of the sea for generating power utilizing a shallow water wave. The system comprises a mooring located either in the sea or at the sea bottom, a chain having one end connected with the mooring and the other end to which a dead-weight is attached. A float is provided with a generator and a rotary member for rotating engaged with the chain. Rotary force of the rotary member produced when the float moves up and down according to an up-and-down motion of the wave is transmitted to the generator, thereby to generating power.
U.S. Pat. No. 7,453,165 to Hench “Method and apparatus for converting ocean wave energy into electricity” discloses a method for harnessing power associated with ocean waves and converting that power into electricity. The apparatus is a buoy that houses a vertically oriented central shaft, a pendulum, and a generator. As the buoy tilts from the vertical under the influence of wave motion, the pendulum is accelerated and rotates about the central shaft. A centrally placed generator is mechanically is driven by the rotating pendulum so that the pendulum's kinetic energy is converted into electricity.
The prior art systems are not capable of producing cost-effective, utility-scale power output to meet modern energy needs.
What is needed is a power-generating device for capturing power from ocean wave motion that provides a stable platform and allows the mechanically linked floats (or buoys) to have maximum exposure to wave action and thereby energy capture.
It is further desirable to provide a method of capturing energy from ocean waves that is efficient, cost effective to manufacture and maintain and is capable of withstanding severe weather events.
It is desirable to have a method and apparatus that is scalable to gain economies in deployment and servicing of the wave energy converter.
It is desirable to provide a method and apparatus of placing a wave energy converter in such a configuration that it is capable of being transported to and from port without interference with ocean navigation.
It is also desirable for the wave energy converter to have an active yaw system to enable optimum/maximum exposure to oncoming waves to maximize energy capture.
The invention relates to an apparatus for generating power utilizing ocean waves. According to one aspect of the invention a plurality of force-transmitting floating pods (buoys) engage a rotary shaft. The rotary shaft drives a generator. The rotary shaft produces a rotary force when the pods move up and down according to an up-and-down motion of an ocean wave. The rotary force is transmitted to the generator to thereby cause the generator to generate power.
In accordance with another of the invention, a hydraulic system provides for energy capture in both upward and downward pod motion.
According to the invention floating pods are used which are moving in an up-and-down motion as the waves pass. The pods are coupled or connected to a lever assembly, for example an arm made of a rigid material. The pods are arranged along an elongated base, which may be an open lattice structure allowing waves to pass through it to activate the pods on the opposite side. The length of the base and the number and size of the pods depend on the expected frequency, wavelength, and amplitude of the waves in the target area. The base may be long enough to straddle a multiple of waves, e.g. 2 to 3 long waves thereby minimizing “pitching” of the base, allowing maximum energy capture by the pods. Along the base (e.g. a V-shaped or Box Shape structure), a number of the power generating components are placed. In the case of a mechanical coupling between the arm/lever of the pods and the power generating system the torque transmitting shafts extend along the elongated base. There may be multiple bases rigidly coupled together in order to build a structure extending over several long waves. In the case of a coupling of the arms/levers of the pods to a hydraulic system the base comprises or houses hydraulic cylinders, which are actuated by the force exerted by the moving pods and transmitted by the arms/levers. The base therefore provides a point of application of the leverage force since it does not follow the up-and-down motion of the waves in the same way as the pods. Since the base extends over at least a considerable part of the wavelength of the waves (or even over more than one wavelength) the forces acting on the base are always different from those acting on a single pod (which is extends only over a small fraction of the wavelength). Therefore the pods are moving up and down relative to the base. Since the arms/levers of the pods are coupled to the base so that they are pivotable, they can exert a leverage force on the force transmitting elements.
It is therefore one key feature of the invention to couple a multiple of pods to a common open lattice structure. Since the structure extends over a full wavelength or more than one wavelength, different pods do experience different wave heights or amplitudes. This means the structure as such does not follow the wave motion as the pods do. This gives rise to a relative movement of the pods and the rest of the structure, which in turn is converted into a leverage force and further in rotational torque or into hydraulic pressure.
The structure will actively yaw to be at an angle (˜45°) to the oncoming waves in order to optimize exposure to the wavefront and period between waves for minimum pitching and maximum energy capture. As wave direction changes, the system will yaw accordingly.
The base may comprise passive floating elements itself in order to provide for buoyancy. However, the base may also be supported solely by means of the pods coupled to the base.
The pods may be made of any appropriate material, which can stand seawater and mechanical stress. The shape of the pods is optimized for wave lift and travel. The pods may be rotated relative to their attached arms (or levers) to facilitate towing from port to the deployment site, or to minimize wave loading under extreme sea states. The pods may have a chamber that can be flooded to allow the entire wave converter system to submerge below potentially damaging wave orbitals.
Along the base the pods may be arranged on two opposite sides of the base thereby keeping the base in balance and providing for a counterforce against the pods on the other side of the base. The open lattice base to which the pods are attached allows waves to pass through the base structure to freely activate pods on the opposite side.
The design and operational approach according to the invention avoids structural concepts requiring extensive use of structural materials to resist bending, hogging, and torsion loads to sustain extreme wave loads from the 50-year return wave. The invention does this by providing a compliantly moored backbone structure, with the pods riding on the waves. While some of the loads get transferred to the backbone, the power conversion system controls these loads by providing the pods less and less resistance as the wave height increases (resulting in a constant power output). Another method to withstand extreme wave loads is to partially flood the pods and allow the wave converter system to submerge to a depth out of the range of the extreme surface wave forces. As the extreme sea state normalizes, the flooded pods are charged with air pressure to evacuate the seawater, and the system resurfaces.
Due to the length of the structure the pitching in minimized which in turn leads to greater energy capture of the apparatus.
In accordance with yet another aspect of the invention a hydraulic system controls the movement of the pods by using the energy of a wave to activate the hydraulic system and a hydraulic turbine such as an impulse turbine or hydraulic motor connected to an electric generator.
In accordance with a further aspect of the invention the hydraulic system includes an impulse turbine and a impulse turbine nozzle in circuit with a pod hydraulic system, which automatically adjusts the force required to move the pods by the waves with changing wave heights.
In accordance with a further aspect of the invention, the pods and shaft are assembled in lengths that result in a stable center structure enabling maximum usable pod displacement and hence energy capture from ocean waves.
In accordance with a further aspect of the invention, the pods impart pumping force in both the upward and downward wave motion using a double-acting piston pump to pressurize hydraulics allow for energy capture.
The invention has the advantage that the modular units allow for cost-effective manufacturing and deployment and tailoring of total power per device, given the needs and resources at the site.
The invention has the advantage that the units assembled to lengths that result in a stable center structure enabling maximum usable pod displacement and hence energy captured from the waves.
The invention has the advantage that the system uses soft-stop hydraulics for piston throw.
The invention has the advantage that a cable-stayed structure version of the design in the center, or base structure, results in cost and weight savings.
The invention has the advantage that the pod hydrodynamic and hydrostatic shape is optimized for low cost of energy (maximizing lifting and dropping forces while minimizing undesired loads, lift force from wave orbitals) and may be rotated at the attachment to the arm to minimize drag during towing to the deployment site, to minimize exposure to waves during extreme wave events.
The invention has the advantage that the tubular base structures double as a hydraulic accumulator to level output. The tubular structure may also serve as ballast, and or pressurized air tanks to clear flooded pods of seawater to resurface the submerged system once extreme wave conditions subside.
The invention has the advantage that the pod variable lift and drop forces maximize energy capture.
The invention has the advantage that system enables multi-directional and frequency energy capture.
The invention has the advantage that the yaw system provides for an individual unit and collective units in an array to manage changes in direction of wind and/or wave travel to maximize energy capture.
The invention has the advantage that mooring systems employed share mooring points, reducing costs